The present invention concerns a method, and the relative device, for bending and shaping, also of the type with a possibly varying radius, at least partly plane elements of a deformable type, such as panels, metal sheet, plates or suchlike, made by means of a bending machine, in order to obtain a panel shaped according to a pre-established design or project.
Bending machines are known by means of which a plane element of deformable type, for example a metal sheet, is bent to obtain a shaped element according to a pre-established project. Conventional machines substantially comprise a supporting plane on which the sheet to be bent is arranged, a sheet-pressing element suitable to clamp on each occasion a segment of the sheet against the supporting plane, and a bending assembly that acts on a free portion of the sheet adjacent to the segment clamped by the aforesaid element.
The bending assembly normally comprises two opposite blades mounted on a blade-bearing element that is driven in one direction or the other according to whether the bend to be made is upwards or downwards.
Conventional machines are also equipped with a system to set the angle of bend that allows to set in advance a sequence of angles of bend to be made according to the project to be made.
One disadvantage of conventional bending machines is the lack of reliable control means that allow to verify that the angle of bend achieved coincides with the pre-set angle of bend. In fact it is known that, after it has been subjected to bending, a segment of sheet tends to return elastically back by a certain angle, and this causes a reduction in the real value of the angle of bend with respect to the angle set.
The elastic return, to be more exact, is a variable that depends on many parameters, for example the size and thickness of the sheet, the intrinsic elasticity, the mechanical resistance, the production lot, the value of the angle of bend, environmental conditions, and others.
To be able to correct the deviation of the actual value from the project value, at least the first sheet bent must therefore be removed from the machine, to measure the actual value of bending, and then returned to the machine to perform the bending. In the case of particular or difficult bends, it often happens that some first panels must be eliminated because they are incorrectly bent in a way that cannot be remedied.
Such systems therefore have the disadvantage that they require burdensome and complex operations to obtain a precision bending, which entails a loss of time, longer processing times and additional costs, especially in the case where a sequential processing of sheets of different elasticity and thickness is intended.
There are also visual systems that provide to record the bending zone to verify deviations with respect to the project angle, but such systems are of an artisan nature and rely on the ability and experience of the operator.
For example, an optical light beam device for automatically controlling the bending operation when bending with a press brake is known from U.S. Pat. No. 4,772,801. Such optical light beam device comprises an emitter, mounted on one side of the press, adapted to produce a large-diameter light beam, directed parallel to the bending axis of the workpiece to be bent, and a receiver comprising a screen drilled with a plurality of holes arranged to forming a plurality of light beams of small diameters. A microordinator is connected to the receiver and permits the determination of the instantaneous bending angle of the workpiece and the control of the descent of the punch.
WO 96/21529, on which the preamble of claims 1 and 11 is based, also discloses a profile definition system for use with profile bending apparatus using an imaging process. A profile such as that used to form a cutting knife is located above a non-reflective surface such that the profile configuration can be imaged through a camera substantially mounted above it. The camera image is captured by a frame grabber device such that the profile configuration can be compared in comparator means with a desired profile shape. Dependent upon the comparison further profile strip feed and/or bend operations may be performed in order to bring into substantial agreement the actual strip profile and the desired strip profile.
However, both documents cited disclose systems which permit only to calculate a bending angle correction and operate the bending machine accordingly in order to match the actual shape and the required shape of the bent element. Neither of these documents discloses or suggests any systems able to acquire, for each bending operation, data related to the offsets between the bend made and the bend required for influencing the driving of the bending device so as to obtain the desired values of the bend to be made automatically, and without any human intervention.
Moreover, in both documents, after each bending step the element being bent is completely released by the bending assembly, so that it is impossible to guarantee a reliable reference for the next bends to be made.
The present Applicant has devised and embodied this invention to overcome the shortcomings of the state of the art, and to obtain other advantages.